Referring to FIG. 1, a main transmission 10 for a Sikorsky Aircraft Corporation BLACK HAWK.RTM. (BLACK HAWK.RTM. is a registered trademark of the Sikorsky Aircraft Corporation) helicopter (not shown) is depicted in mechanical connectivity with a main rotor drive shaft 12 and a tail take-off flange 14 which is, in turn, connected to a tail rotor drive shaft (not shown). The main transmission 10 contains dual inputs 16 for connecting a pair of turbine engines (not shown) to the main transmission 10, wherein the turbine engines provide torque to the main rotor drive shaft 12 and the tail take-off flange 14 through gearing arrangements (not shown) within the main transmission 10. In addition, a rotor brake assembly 18 is disposed in combination with the main transmission 10, wherein the rotor brake assembly 18 is operable, upon actuation, to arrest rotation of both the main rotor drive shaft 12 and the tail take-off flange 14. However, the configuration of the prior art rotor brake assembly 18 is such that the rotor brake assembly 18 is only capable of arresting rotation of the main rotor drive shaft 12 and the tail take-off flange 14 subsequent to both of the turbine engines being shut-down.
Referring to FIGS. 2 and 3, the prior art rotor brake assembly 18 comprises a split design having a first caliper 20 connected to a second caliper 22 with a plurality of bolts 24. Each caliper 20, 22 includes recesses 26 therein for housing a plurality of hydraulically-actuated pucks 28. The calipers 20, 22 are internally configured for facilitating the flow of hydraulic fluid (not shown) to each of the plurality of hydraulically-actuated pucks 28, wherein the hydraulic fluid is supplied to the calipers 20, 22 through a hydraulic fluid input conduit 34 connected to the first caliper 20. A plurality of aligned apertures 36 are provided in the calipers 20, 22 for facilitating the flow of hydraulic fluid therebetween.
A brake disc 38 is disposed in combination with the calipers 20, 22 such that an arcuate region 40 of the brake disc 38 is interposed between the plurality of hydraulically-actuated pucks 28. The brake disc 38 is mechanically connected to the main transmission 10 such that the brake disc 38 can be urged into rotational movement about an axis 42 in response to torque provided by the main transmission 10. Upon introduction of hydraulic fluid into the calipers 20, 22, the plurality of hydraulically-actuated pucks 28 are actuated such that they are urged into abutting engagement with the arcuate region 40 of the brake disc 38, thereby generating frictional forces therebetween and arresting the rotational movement of the brake disc 38. In operation, the mechanical connectivity between the main transmission 10 and the brake disc 38 is such that arresting the rotation of the brake disc 38 results in an arrestation of the rotational movement of the main rotor drive shaft 12.
As noted above, the prior art rotor brake assembly 18 is only capable of arresting rotation of the main rotor drive shaft 12 subsequent to the turbine engines being shutdown. This is due to the fact that if one or both of the turbine engines are at ground idle, the prior art rotor brake assembly 18 would not be able to react the loads or effectively dissipate the heat generated by an attempt to arrest the rotation of the brake disc 38.
However, there are certain situations wherein it would be advantageous if at least one of the turbine engines was kept at ground idle while the rotational movement of the main rotor drive shaft 12 is arrested. One such situation is when a helicopter lands, e.g. to unload and/or take-on passengers, and then takes off within a relatively short period of time. In that situation, it would be advantageous to keep at least one turbine engine at ground idle such upon release of the rotor brake assembly 18, the main rotor drive shaft 12 would resume rotation, and the other turbine engine could be assisted during its power-up, thereby reducing the time required for getting the main rotor drive shaft 12, and thereby the main rotor blades (not shown) up to the desired rotational speed.